1. Field of the Invention
The present invention relates to an ink ribbon take-up mechanism for taking up an ink ribbon in a ribbon cassette which is loaded onto a carriage of a printer.
2. Description of the Related Art
FIG. 6 shows a principal portion of a conventional thermal transfer printer. As shown in the same figure, a flat plate-like platen 42 is disposed at an approximate center of a frame of a printer 41 in such a manner that a printing surface thereof is substantially vertical. In front of the platen 42 of the frame is disposed a carriage shaft 43 at a lower position and in parallel with the platen 42. Onto the carriage shaft 43 is mounted a carriage 44 so that it can reciprocate along the carriage shaft 43. At a front end portion of the carriage 44 is mounted a thermal head 45 in an opposed relation to the platen 42. On the upper surface of the carriage 44 are disposed a take-up bobbin 47 for taking up an ink ribbon R housed within a ribbon cassette 46 and a delivery bobbin 48 delivering the ink ribbon R. The ribbon cassette 46 is loaded onto the carriage 44 so that the ink ribbon R received therein is guided to between the thermal head 45 and the platen 42. Further, on the upper surface of the carriage 44 is disposed a second take-up bobbin 49 rotatably on a downstream side of the thermal head 45 in the traveling path of the ink ribbon R, while on an upstream side of the thermal head is disposed a second delivery bobbin 50 rotatably.
FIG. 7 shows a principal portion of a conventional ink ribbon take-up mechanism, in which an outwardly projecting support flange 52 is formed integrally at a lower end portion of a take-up shaft 51, and a take-up gear 53 is fitted on the lower end portion of the take-up shaft 51 in a rotatable manner independently of the take-up shaft 51. A felt member 54 serving as a frictional slide mechanism is interposed between the take-up gear 53 and the support flange 52 of the take-up shaft 51. Onto an upper end portion of the take-up shaft 51 is fixed a take-up bobbin 47 which is exposed to the upper surface of the carriage 44 and which is brought into engagement with a shaft hole 65 formed in a core 55 of the ribbon cassette 46. On the outer peripheral surface of the take-up bobbin 47 are formed a plurality of engaging projections 56 circumferentially at equal intervals, while in the underside of the take-up bobbin 47 is formed an annular retaining ring 57. On the outer periphery side of the take-up shaft 51 is disposed a biasing spring 58 whose upper end portion is anchored in the retaining groove 57 of the take-up bobbin 47 and whose lower end portion is in abutment with the upper surface of the take-up gear 53. With the biasing force of the biasing spring 58, the take-up gear 53 is brought into pressure contact with the support flange 52 of the take-up shaft 51 through the felt member 54.
As shown in FIG. 8, a drive gear 61 fixed onto a rotating shaft 60 of a take-up motor for the ink ribbon R is in mesh with the take-up gear 53. The drive gear 61 is rotated by rotation of the take-up motor 59 for the ink ribbon R, thereby causing the take-up gear 53 to rotate. As a result, with a frictional force of the felt member 54 created by the biasing force of the biasing spring 58 of the take-up gear 53, the rotative driving force is transmitted to the take-up shaft 51. The take-up shaft 51 is supported rotatably on a support shaft 51A whose base end portion is fixed to the carriage 44.
On the other hand, the ribbon cassette 46 loaded onto the upper surface of the carriage 44 is constructed as in FIG. 9 in which, in the interior of a case body 62 which is generally rectangular in plan, are disposed a pair of cores 55, 55 supported rotatably, a pair of pinch rollers 63, 63 supported rotatably for peeling off the ink ribbon, and a plurality of guide rollers (not shown) supported rotatably and facing the ribbon traveling path.
The paired cores 55, 55 are formed in a generally cylindrical shape and both ends of the ink ribbon R, which is a heat-subliming or heat-melting ink ribbon, are wound round the outer peripheral surfaces of the cores 55, 55, respectively. When the ribbon cassette 46 is loaded onto the carriage 44 of the printer used, one of the paired cores 55, 55 comes into engagement with the take-up bobbin 47 and serves as a take-up core 55A for taking up the portion, which has been used for printing, of the ink ribbon R, while the other core 55 comes into engagement with the delivery bobbin 48 and serves as a feed core 55B which feeds the ink ribbon R for printing. As to the pinch rollers, one pinch roller 63A comes into engagement with the second take-up bobbin 49 and provides a peeling force for the ink ribbon R during printing, while the other pinch roller 63B comes into engagement with the second delivery bobbin 50 and acts to impart a peeling torque to the ink ribbon.
In the inner peripheral surface of each core 55 are formed a plurality of engaging grooves 64 in a splined shape circumferentially at predetermined intervals. The inside of the inner peripheral surface of each core 55 define the shaft hole 65 for engagement with the take-up bobbin 47 or the delivery bobbin 48 formed on the carriage 44 of the printer.
In the conventional printer 41 described above, paper is inserted from a paper insertion port (not shown) formed behind the platen 42 and is conveyed in a direction perpendicular to the moving direction of the carriage 44 at a predetermined speed by means of a paper conveying mechanism (not shown). On the other hand, the thermal head 45 is brought into pressure contact with the paper at a predetermined pressure. In this state, the carriage 44 is moved and the take-up bobbin 47 is rotated to take up the ink ribbon R in the ribbon cassette 46, while the thermal head 45 is driven in accordance with a desired printing signal to effect a desired printing for the paper.
Thus, in the above ink ribbon take-up mechanism, the take-up shaft 51 itself is rotated to rotate the core 55A for functioning as a take-up core of the ribbon cassette 46, through the engaging projections 56 formed on the outer peripheral surface of the take-up bobbin 47 fixed to the upper end portion of the take-up shaft 51 and also through the engaging grooves 64 formed in the inner peripheral surface of the associated core 55 of the ribbon cassette, thereby taking up the ink ribbon R around the outer periphery of the core 55A.
The structure of the second ink ribbon take-up mechanism, which corresponds to the portion of the second take-up bobbin 49 engaged with the associated pinch roller 63 of the ribbon cassette 46, has also been the same as that of the ink ribbon take-up mechanism described above.
However, since the outside diameter of the support shaft 51A in the conventional ink ribbon take-up mechanism is as small as 1.6 mm or so, there has been an inconvenience such that when taking up the ink ribbon R, the support shaft 51A is inclined or bent by being pulled with the tension working on the ink ribbon R. If the support shaft 51A rotates in an inclined state, the core 55A (pinch roller 63) engaged with the take-up bobbin 47(second take-up bobbin 49) may be inclined, making it impossible to effect a stable traveling of the ink ribbon.
Further, between the support shaft 51A and the take-up shaft 51 there is a clearance for making both shafts rotatable and between the take-up shaft 51 and the core 55A (pinch roller 63) there also is a clearance for insertion and engagement with respect to each other, so that the core 55A has a large wobbling. Consequently, the traveling of the ink ribbon R sometimes becomes unstable. It turned out that for improving the print quality it is necessary to stabilize the traveling of the ink ribbon and the take-up load and that therefore it is necessary to suppress inclination and wobbling of the core 55A (pinch roller 63).